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                                                                   L. Martin
     S/MIME Working Group                                       M. Schertler
     Internet Draft                                         Voltage Security
     Expires: April 2007                                        October 2006
     
     
     
         Using the Boneh-Franklin and Boneh-Boyen identity-based encryption
               algorithms with the Cryptographic Message Syntax (CMS)
     
     
                          <draft-ietf-smime-bfibecms-01.txt>
     
     
     Status of this Document
     
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     Abstract
     
        This document describes the conventions for using the Boneh-Franklin
        (BF) and Boneh-Boyen (BB1) identity-based encryption algorithms in
        the Cryptographic Message Syntax (CMS) to encrypt content encryption
        keys. Object identifiers and the convention for encoding a
        recipient's identity are also defined.
     
     
     
     
     
     
     

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     Table of Contents
     
     
        1. Introduction...................................................2
           1.1. Terminology...............................................3
        2. Using identity-based encryption................................3
        3. Algorithm object identifiers...................................6
        4. Processing by the sender.......................................6
        5. Processing by the receiver.....................................7
        6. ASN.1 Module...................................................8
        7. Security Considerations........................................9
           7.1. Attacks that are outside the scope of this document.......9
           7.2. Attacks that are within the scope of this document........9
           7.3. Attacks that the protocols defined in this document are
           susceptible to................................................10
           7.4. Attacks that the protocols defined in this document protect
           against.......................................................10
        8. IANA Considerations...........................................10
        9. References....................................................11
           9.1. Normative References.....................................11
        Authors' Addresses...............................................12
        Intellectual Property Statement..................................12
        Disclaimer of Validity...........................................12
        Copyright Statement..............................................13
        Acknowledgment...................................................13
     
        1. Introduction
     
        This document defines the steps needed to use the Boneh-Franklin [BF]
        and Boneh-Boyen [BB1] identity-based encryption (IBE) public-key
        algorithms in the Cryptographic Message Syntax (CMS) [CMS]. IBE is a
        public key technology for encrypting content-encryption keys (CEKs)
        that can be implemented within the framework of the CMS: the
        recipient's identity is incorporated into the EnvelopedData CMS
        content type using the OtherRecipientInfo CHOICE in the RecipientInfo
        field as defined in section 6.2.5 of [CMS]. This document does not
        describe the implementation of the BF and BB1 algorithms, which are
        described in detail in [IBCS].
     
        IBE algorithms are a type of public-key cryptographic algorithm in
        which the public key is calculated directly from a user's identity
        instead of being generated randomly. This requires a different set of
        steps for encryption and decryption than would be used with other
        public-key algorithms, and these steps are defined in Sections 4 and
        5 of this document respectively.
     
     
     
     
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        This document also defines the object identifiers and syntax of the
        object that is used to define the identity of a message recipient.
     
        CMS values and identity objects are defined using ANS.1 [ASN1].
     
        1.1. Terminology
     
        The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
        "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
        document are to be interpreted as described in RFC-2119 [KEYWORDS].
     
        2. Using identity-based encryption
     
        To use IBE, the OtherRecipientInfo field MUST be set to an
        IBEOtherRecipient type.
     
        IBEOtherRecipientInfo ::= SEQUENCE {
          ibeORIType      OBJECT IDENTIFIER,
          ibeORIValue     IBERecipientInfo
        }
     
        The fields of IBEOtherRecipientInfo have the following meanings:
     
        ibeORIType defines the object identifier (OID) that indicates that
        the subsequent ibeORIValue is the information necessary to decrypt
        the message using IBE. This field MUST be set to
     
        ibeORIType OBJECT IDENTIFIER ::= { joint-iso-itu(2) country(16)
          us(840) organization(1) identicrypt(114334) ibcs(1)
          cms(4) ori-oid(1) }
     
        ibeORIValue defines the identity that was used in the IBE algorithm
        to encrypt the CEK. This is an IBERecipientInfo type.
     
        IBERecipientInfo ::= SEQUENCE {
          cmsVersion         INTEGER { v3(3) },
          keyFetchMethod     OBJECT IDENTIFIER,
          recipientIdentity  IBEIdentityInfo,
          serverInfo         SEQUENCE OF OIDValuePairs OPTIONAL,
          encryptedKey       EncryptedKey
        }
     
        The fields of IBERecipientInfo have the following meanings:
     
        The cmsVersion MUST be set to 3.
     
     
     
     
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        The keyFetchMethod is the OID that defines the method of retrieving
        the private key that the recipient MUST use. How to retrieve an IBE
        private key using the steps defined in [IBE] is defined by the
        keyFetchMethod OID. The method for retrieving private keys that is
        specified in [IBE] is defined by cmsPPSOID.
     
        cmsPPSOID OBJECT IDENTIFIER ::= { joint-iso-itu(2) country(16)
          us(840) organization(1) identicrypt(114334) pps-schemas(3)
          ic-schemas(1) pps-uri(1)
        }
     
        The recipientIdentity is the data that was used to calculate the
        public key that was used to encrypt the CEK. This MUST be an
        IBEIdentityInfo type. This recipientIdentity is used to calculate IBE
        public and private keys as described in [IBCS].
     
        IBEIdentityInfo ::= SEQUENCE {
          District        UTF8STRING,
          Serial          INTEGER,
          identitySchema  OBJECT IDENTIFIER,
          identityData    OCTET STRING
        }
     
        The fields of IBEIdentityInfo have the following meanings.
     
        The district and serial are unique identifiers that are used to
        construct the URI for the location of where the IBE public parameters
        are located. The construction and use of this URI is defined in
        [IBE].
     
        The identitySchema defines the format that is used to encode the
        information that defines the identity of the recipient. This MUST be
        set to cmsIdentityOID.
     
        cmsIdentityOID OBJECT IDENTIFIER ::= { joint-iso-itu(2) country(16)
           us(840) organization(1) identicrypt(114334) keyschemas(2)
           icschemas(1) rfc822email(1)
        }
     
        The identityData is the identity of the recipient. For use in S/MIME,
        this MUST be an EmailIdentitySchema type which is DER encoded. Other
        applications MAY use other formats for the identityData.
     
     
     
     
     
     
     
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        EmailIdentitySchema ::= SEQUENCE {
          rfc822Email UTF8STRING,
          time        GeneralizedTime
        }
     
        The rfc822Email is the DER-encoded e-mail address of the recipient in
        the format defined by [RFC822].
     
        The value of "time" is the DER-encoded UTC time after which the
        sender wants to let the recipient decrypt the message, so it may be
        called the "not-before" time. This is usually set to the time when
        the message is encrypted, but MAY be set to a future time. UTC time
        values are expressed to the nearest second.
     
        The sender of an IBE-encrypted message may want to express this time
        rounded to a larger time interval to create a key lifetime and reduce
        the number of IBE private keys that a recipient needs to retrieve.
        Based on the time interval chosen a recipient would only have to
        retrieve a new IBE key once during the interval. To do this, follow
        the following steps. Let "time-interval" be the number of seconds in
        this larger time interval.
     
           1. Find the GeneralizedTime for the not-before value.
     
           2. Convert this GeneralizedTime into the number of seconds since
     
              January 1, 1970. Call this "total-time."
     
           3. Calculate reduced-time = ( floor(total-time /
     
              time-interval) ) * time-interval.
     
           4. Convert reduced-time to a GeneralizedTime to get the not-before
        "time" value.
     
        An example of this algorithm for computing a one week time interval
        is:
     
           1. Say the GeneralizedTime is 20020401000000Z
     
           2. The total-time is 1017612000
     
           3. A time-interval of 1 week is 604800 seconds. So the reduced-
          time = (floor(1017612000/604800))* 604800 = 1017273600
     
           4. Giving the reduced-time GeneralizedTime for a 1 week time
          interval of 20020328000000Z
     
     
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        3. Algorithm object identifiers
     
        The BF and BB1 algorithms as defined in [IBCS] have the following
        object identifiers:
     
        bf OBJECT IDENTIFIER ::= { joint-iso-itu(2) country(16) us(840)
           organization(1) identicrypt(114334) ibcs(1) ibcs1(1)
           ibe-algorithms(2) bf(1) }
     
        This is the object identifier that MUST be inserted in the
        keyEncryptionAlgorithm field in the CMS when the BF algorithm is used
        to encrypt the CEK.
     
        bb1 OBJECT IDENTIFIER ::= { joint-iso-itu(2) country(16) us(840)
           organization(1) identicrypt(114334) ibcs(1) ibcs1(1)
           ibe-algorithms(2) bb1(2) }
     
        This is the object identifier that MUST be inserted in the
        keyEncryptionAlgorithm field in the CMS when the BB1 algorithm is
        used to encrypt the CEK.
     
        4. Processing by the sender
     
        The sender of a message that uses IBE to encrypt content encryption
        keys performs the following steps:
     
           1. Selects a set of IBE public parameters to use in the subsequent
        steps in accordance with his local security policy. He then
        determines the URI where the public parameters can be obtained using
        the process described in [IBE]. This information MUST be encoded in
        the IBEIdentityInfo as described in Section 2.
     
           2. Sets the fields of an OtherRecipientInfo object to their
        appropriate values as described in Section 2.
     
           3. Calculates an IBE public key as defined in [IBCS] using this
        IBEIdentityInfo as the identity information.
     
           4. This IBE public key is then used to encrypt the content
        encryption key (CEK), using the algorithms that are defined in
        [IBCS].
     
           5. Sets encryptedKey to the IBE-encrypted CEK.
     
           6. Within the CMS, keyEncryptionAlgorithm MUST then be set to the
        appropriate OID for the IBE algorithm that was used (see Section 3).
     
     
     
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        5. Processing by the receiver
     
        Upon receiving a message that has a CEK encrypted with IBE, the
        recipient performs the following steps to decrypt the CEK:
     
           1. Determines that the CEK is IBE-encrypted by noting that the
             oriType of the OtherRecipientInfo type is set to ibeORIType.
     
           2. Determines that the recipientIdentity was used as the identity
             in IBE encryption of the CEK.
     
           3. Determines the location of the IBE public parameters and the
             IBE Private Key Generator as described in [IBE].
     
           4. Obtains the IBE public parameters from the location determined
             in Step 3 using the process defined in [IBE].
     
           5. Obtains the IBE private key needed to decrypt the encrypted CEK
             using the process defined in [IBE].
     
           6. Decrypts the CEK using the IBE private key obtained in Step 4
             using the algorithms described in [IBCS].
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
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        6. ASN.1 Module
     
        IBECMS-module { joint-iso-itu(2) country(16) us(840) organization(1)
          identicrypt(114334) ibcs(1) cms(4) module(5) version(1)
        }
     
        DEFINITIONS IMPLICIT TAGS ::= BEGIN
     
        IBEOtherRecipientInfo ::= SEQUENCE {
          oriType   OBJECT IDENTIFIER,
          oriValue  IBERecipientInfo
        }
     
        ibeORIType OBJECT IDENTIFIER ::= { joint-iso-itu(2) country(16)
          us(840) organization(1) identicrypt(114334) ibcs(1)
          cms(4) ori-oid(1)
        }
     
        IBERecipientInfo ::= SEQUENCE {
          cmsVersion         INTEGER { v3(3) },
          keyFetchMethod     OBJECT IDENTIFIER,
          recipientIdentity  IBEIdentityInfo,
          serverInfo         SEQUENCE OF OIDValuePairs OPTIONAL,
          encryptedKey       EncryptedKey
        }
     
        IBEIdentityInfo ::= SEQUENCE {
          District        UTF8STRING,
          serial          INTEGER,
          identitySchema  OBJECT IDENTIFIER,
          identityData    OCTET STRING
        }
     
        OIDValuePairs ::= SEQUENCE {
          fieldID     OBJECT IDENTIFIER,
          fieldData   OCTET STRING
        }
     
        EmailIdentitySchema ::= SEQUENCE {
          rfc822Email  UTF8STRING,
          time         GeneralizedTime
        }
     
        cmsIdentityOID OBJECT IDENTIFIER ::= { joint-iso-itu(2) country(16)
          us(840) organization(1) identicrypt(114334) keyschemas(2)
          icschemas(1) rfc822email(1)
        }
     
     
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        cmsPPSOID OBJECT IDENTIFIER ::= { joint-iso-itu(2) country(16)
          us(840) organization(1) identicrypt(114334) pps-schemas(3)
          ic-schemas(1) pps-uri(1)
        }
     
        END
     
        7. Security Considerations
     
        This document is based on [CMS] and [IBCS], and the relevant security
        considerations of those documents apply. In addition, the following
        considerations that are particular to this document.
     
          7.1. Attacks that are outside the scope of this document
     
        Attacks on the cryptographic algorithms that are used to implement
        IBE are outside the scope of this document. Such attacks are detailed
        in [IBCS], which defines parameters that will give the equivalent of
        80-bit security, 112-bit security and 128-bit security. We assume
        that competent administrators of an IBE system will select parameters
        that provide a sufficient resistance to cryptanalytic attacks by
        adversaries.
     
        Attacks that require access to machines used by either the client or
        the server components defined in this document are also outside the
        scope of this document. Attacks that give an attacker the ability to
        access or change the information on a PPS or PKG, especially the
        cryptographic material, will defeat the security of an IBE system. To
        address this concern, the PPS and PKG servers SHOULD be configured in
        accordance with best current practices [NIST]. An IBE system should
        be operated in an environment where such illicit access is infeasible
        for attackers to obtain.
     
        We also assume that all administrators of a system implementing the
        protocols that are defined in this document are trustworthy and will
        not abuse their authority to bypass the security provided by an IBE
        system. Similarly, we assume that users of an IBE system will behave
        responsibly, not sharing their authentication credentials with
        others. Thus attacks that require such assumptions are outside the
        scope of this document.
     
          7.2. Attacks that are within the scope of this document
     
        Attacks that passively monitor information transmitted between users
        of an IBE system and the PPS and PKG are within the scope of this
     
     
     
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        document, as are attacks that let an adversary masquerade as a PPS or
        PKG are also within the scope of this document.
     
          7.3. Attacks that the protocols defined in this document are
             susceptible to
     
        The protocols defined in this document do not explicitly defend
        against an attacker masquerading as a legitimate IBE PPS or PKG. To
        provide protection against this possibility, client software that
        implements the protocols defined in this document SHOULD have a user
        interface that allows users to view the details of connections to PPS
        and PKG servers so that users cannot easily be tricked into providing
        valid authorization credentials to an attacker.
     
        The protocols defined in this document are also vulnerable to Denial
        of Service attacks against an IBE PPS or PKG. DOS attacks against
        either component can result in users unable to access the information
        and services required to encrypt or decrypt using IBE, and users of
        an IBE system SHOULD take the appropriate countermeasures [RFC2827,
        RFC3882] that their use of IBE requires.
     
          7.4. Attacks that the protocols defined in this document protect
             against
     
        All communications between users of an IBE system and the PPS or PKG
        are encrypted using SSL 3.0 [SSL] or TLS 1.1 [TLS], which should
        provide an adequate level of protection for such communications.
     
        The authentication method used by an IBE PKG should also be
        sufficiently strong to prevent attackers from easily guessing them
        through trial and error.
     
        8. IANA Considerations
     
        All of the object identifiers used in this document were assigned by
        the National Institute of Standards and Technology (NIST), so no
        further action by the IANA is necessary for this document.
     
     
     
     
     
     
     
     
     
     
     
     
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        9. References
     
        9.1. Normative References
     
        [ASN1] CCITT, Recommendation X.209: Specification of Basic Encoding
                  Rules for Abstract Syntax Notation One (ASN.1). 1998.
     
        [CMS] R. Housley, "Cryptographic Message Syntax," RFC 3369, August
                  2002.
     
        [IBCS] X. Boyen, L. Martin, "Identity-based cryptography standard
                  (IBCS) #1: supersingular curve implementations of the BF
                  and BB1 cryptosystems," draft-ieft-martin-ibcs-00.txt.
     
        [IBE] G. Appenzeller, L. Martin, M. Schertler, "Identity-based
                  Encryption Architecture," draft-ietf-ibearch-01.txt.
     
        [KEYWORDS] S. Brander, "Key Words for Use in RFCs to Indicate
                  Requirement Levels," BCP 14, RFC 2119, March 1997.
     
        [NIST] M. Souppaya, J. Wack, K. Kent, "Security Configuration
              Checklist Program for IT Products - Guidance for Checklist
              Users and Developers," NIST Special Publication SP 800-70, May
              2005.
     
        [RFC822] D. Crocker, "Standard for the format of ARPA internet text
                  messages," RFC 822, August 1982.
     
        [RFC2827] P. Ferguson, D. Senie, "Network Ingress Filtering:
              Defeating Denial of Service Attacks which employ IP Source
              Address Spoofing," RFC 2827, BCP 38, May 2000.
     
        [RFC3882] D. Turk, "Configuring BGP to Block Denial-of-Service
              Attacks," RFC 3882, September 2004.
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
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     Authors' Addresses
     
        Luther Martin
        Voltage Security
        1070 Arastradero Rd Suite 100
        Palo Alto CA 94304
     
        Phone: +1 650 543 1280
        Email: martin@voltage.com
     
        Mark Schertler
        Voltage Security
        1070 Arastradero Rd Suite 100
        Palo Alto CA 94304
     
        Phone: +1 650 543 1280
        Email: mark@voltage.com
     
     
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        This document and the information contained herein are provided on an
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        Copyright (C) The Internet Society (2006).
     
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        Funding for the RFC Editor function is currently provided by the
        Internet Society.
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
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